c. Optionally, enable the µDMA completion interrupt by setting the DMATXIM or DMARXIM bit
in the SSIIM register.
Note: For a TX DMA completion interrupt, software must disable the µDMA transmit enable
to the SSI by clearing the TXDMAE bit in the QSSI DMA Control (SSIDMACTL) register
and then setting the DMATXIC bit in the SSIICR register. This clears the DMA completion
interrupt. When the µDMA is needed to transmit more data, the TXDMAE bit must be
set (enabled) again.
7. If this is the first initialization out of reset, enable the QSSI by setting the SSE bit in the SSICR1
register.
As an example, assume the QSSI must be configured to operate with the following parameters:
■ Master operation
■ Freescale SPI mode (SPO=1, SPH=1)
■ 1 Mbps bit rate
■ 8 data bits
Assuming the system clock is 20 MHz, the bit rate calculation would be:
SSInClk = SysClk / (CPSDVSR * (1 + SCR))
1x10
6
= 20x10
6
/ (CPSDVSR * (1 + SCR))
In this case, if CPSDVSR=0x2, SCR must be 0x9.
The configuration sequence would be as follows:
1. Ensure that the SSE bit in the SSICR1 register is clear.
2. Write the SSICR1 register with a value of 0x0000.0000.
3. Write the SSICPSR register with a value of 0x0000.0002.
4. Write the SSICR0 register with a value of 0x0000.09C7.
5. The QSSI is then enabled by setting the SSE bit in the SSICR1 register.
17.4.1 Enhanced Mode Configuration
If the QSSI module supports the Advanced/Bi-/Quad features, then these modes can be enabled
after initializing the QSSI module. Below is an example of configuring the QSSI to transmit two data
bytes in Advanced SSI mode followed by 2 bytes in Bi-SSI mode:
1. Set the MODE bit to 0x3, and the FSSHLDFM bit to 1 in the SSICR1 register. To operate in the
master mode, program the MS bit to 0. Program the remaining bits in the SSICR0 and SSICR1
register to relevant values.
2. Write one data byte to the TX FIFO; set the EOM bit to 1 and write the second data byte to the
Tx FIFO.
June 18, 20141242
Texas Instruments-Production Data
Quad Synchronous Serial Interface (QSSI)
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